Multi-gun cathode ray tube



April 1, 1958 E. SANFORD MULTI-GUN CATHODE RAY TUBE Filed Nov. 1, 1956 1INVENTbR. EMIL SANFORD ATTCRNEYS United States at H 2,829,291 MULTI-GUNCATHODE RAY TUBE Emil Sanford, Clifton, N. L, assignor to Allen B. DuMont Laboratories, Inc., Clifton, N. J., a corporation of DelawareApplication November 1, 1956, Serial No. 619,713

1 Claim. (Cl. 31370) This invention relates to multi-gun cathode raytubes, and more particularly to a three-gun cathode ray tube for colortelevision presentations.

One form of color television tube utilizes three electron guns which arepositioned at the apices of an equilateral triangle. Since for static(undefiected) conditions the separate beams from the three guns mustconverge at a point on the aperture mask, the beams are caused toconverge by mechanical positioning of the guns. Ideally, the three beamsconverge perfectly at the same point. However, in actuality, this resultis difiicult to achieve, and it is desirable that each beam should beindependently positionable to achieve precise convergence.

individual control of the position of each beam may be readilyaccomplished by a magnetic field which is ordinarily produced by abeam-positioning permanent magnet or electromagnetic coil. In prior arttubes, each beam positioning magnetic field influencedfithe other beams,thus causing an interaction which was undesirable.

Prior art tubes exhibited another disadvantage in that they weresusceptible to filament burn-out, due either beam positioning magneticeither'by a permanent magnet or by an electromagnet. Since there arethree beams, three beam positioning fields are ordinarily used. Fig. 1shows thesepermanent magnets 28, 29 and 30 positioned 120 degrees apart.As is well known, electromagnetic coils may alternatively be utilized.For convenience of adjustment, the permanent magnet is generally in theform of a bar which is held in a mating opening either by threads or byfriction clips. Since the magnetized bar will have a north pole and asouth pole, themagnet may be inserted into the opening so that eitherend may be in proximity with the gun structure. Either end of eachmagnet may therefore be positioned to bring the desired pole into therequired position to achieve the optimum beam positioning effect. Ifelectromagnets are used, the same effects are obtained by reversing andcontrolling the current therethrough.

It may be seen from Fig. 1 that magnet 28 is positioned so that one ofits poles affects beam 21. However, leakage of its magnetic field tendsto afiect beams 22 and 23 also, thus producing the undesirableinteraction to accidental arcing within the tube, or to surges in thefilament voltage.

Therefore, the principal object of my invention is to provide animproved multi-gun cathode ray tube.

Another object of my invention is to provide a multigun cathode ray tubewhich provides truly independent positioning of each individual beam.

A further object of my invention is to provide a multigun cathode raytube which provides greater safety against filament burn-out.

The achievement of these objects and others will be realized from thefollowing specification, taken in conjunction with the drawings, inwhich,

Fig. l is a cutaway presentation of a cathode ray tube utilizing myinvention; and

Fig. 2 illustrates a wiring arrangement for the filaments which obviatesprior burn-out difficulties.

Referring now to Fig. i, there is illustrated in cutaway form a cathoderay tube 10 having a tubular neck portion 12, a funnel portion 14, anapertured mask 16, and

a faceplate 18. Within the neck portion is a three-gun assembly 20 whichproduces electron beams 21, 22 and 23, which are used for producingcolor television images. A deflection coil 24 is mounted on neck portion12 adjacent the funnel portion of the tube, while a color purity device26 is mounted on the neck portion adjacent the gun structure.

' The operation of the color purity device is more fully described in mycopending application entitled Cathode Ray Tube, Serial No. 606,001,filed August 24, 1956. As described in the above mentioned application,the color purity device assures that the converged beams will strike theproper portion of the apertured mask. As has been previously statedhowever, a situation is frequently encountered in which two beams maystrike the convergent point, while the third beam does not. 'In thiscase, the third beam is separately positioned by a previously mentioned.A similar situation exists for the other beam positioning magnets (orcoils).

In order to minimize this undesired interaction of the beam positioningdevices on the electron beams, I introduce shields 31 of magneticmaterial between the various guns. As shown in Fig. 1, these shields maytake the form of arcuate semicylinders which fit together like a threepointed star. These shields may be welded to each other, or to suitableportions of the gun structure or both. They serve to confine themagnetic flux to the desired electron beam, while reducing leakage thatwould afieet the others.

Ideally, the color purity device 26, and the beam positioning magnetsshould be located to afiect the electrons after they have left the guns.

However, due to spatial limitations, other elements occupy thislocation, so the beam positioning takes place within the gun. Since theactual beam movement is extremely small this location is satisfactory,and incidentally affords a convenient method of mounting the magneticshielding material.

In prior art multi-gun cathode ray tubes, the failure of any one gunseriously impaired the operation of the tube. Thus, in the case of acolor television tube, should one gun become inoperative, it wouldbecome impossible to produce that particular color or any other color ofwhich that color is a component. One of the weaknesses of theseguns istheir filaments, which are frequently accidentally exposed to electricalsurges due to arcing, and are always susceptible to mechanical shock. Inthe past, the filament of each gun was separately connected across a 6.3volt source, thus requiring a thin, fragile filament.

Referring now to Fig. 2, it will be seen that I propose to connect thefilaments 32 of the electron guns in series. In this way, each filamentis designed to operate at a voltage of 2.1 volts, and may be of heaviercross section. Each filament is therefore stronger and more resistive tomechanical shock. In addition, a voltage surge is less liable to causeburnout, since it is divided among three heavier filaments instead ofexposing each filament to the surge.

It may be seen that my improved gun structure has several advantages.Having described the principles of my invention, I desire to be limitedonly by the claim granted to me.

What is claimed is:

In a multi-gun cathode ray tube, the combination comprising: threeelectron guns positioned at the apices of an equilateral trianglewherebythree electron beams are Patented Apr. 1, 1958 field which may beobtained produced; means to produce magnetic axis of said tube, eachsaid magnet being individually reversible and positionable-whereby thepole of each magnet may assume a desired spacing from said tube axis; ashield of magnetic material separating each said electron beam from theothers, said shield comprising three arcuate elements of magneticmaterial positioned at the ends of said electron guns, said arcuateelements befields which pri- I marilyaifect the position of a singleelectron beam but ing positioned between a selected electron gun andsaid other electron guns; and filaments for each said electron gun, saidfilaments being connected in serieswhcreby a more rugged filamentstructure to better withstand voltage surges and mechanical shock isprovided.

References Cited in the file of this patent UNITED STATES PATENTS2,170,944 Glass Aug. 29, l936 2,7l9,242 Friend Sept. 27, 1955 2,735,031Woodbridge s- Feb. 14. 1956

